JIRA: https://jira.spring.io/browse/INT-4553 Fixes https://github.com/spring-projects/spring-integration/issues/2628 Fixes https://github.com/spring-projects/spring-integration/issues/2629 - Avoid `size()` calls on the MGS, use `poll()` instead. - Optimize the indexes for the `INT_CHANNEL_MESSAGE` table. Avoid size call when no timeout too. Polishing - PR Comments Missed a doc fix Another missed %PREFIX% Fix underscores Polishing; PR comments; make MGQ extendable. Fix version in doc. * Polishing `@since` * Use diamonds whenever it is possible **Cherry-pick to 5.0.x**